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Porous carbon has been expected to be a potential candidate as a lightweight and efficient microwave absorber. Nano-porous carbon carbonized directly from a walnut shell exhibits narrow microwave absorption frequency bandwidth, while the activation process can adjust the pore structure and optimize the microwave absorption performance. Herein, porous carbon materials were successfully prepared using walnut shells as precursors and ZnCl2 as the activating agent. The superior microwave absorption performances of the as-prepared samples could be attributed to the well-developed pore structures and the enhanced dielectric loss capacities of the samples. The interfacial polarization in the walls of the pores and the defects in the samples significantly contributed to the enhancement of the dielectric loss capacities of the samples. In this work, the broadband microwave absorbing porous carbon exhibited an effective absorption bandwidth (reflection loss ≤ −10 dB) of 7.2 GHz (ranging from 10.8 GHz to 18.0 GHz) when the absorber thickness was 2.5 mm. In addition, an effective absorption bandwidth of 6.0 GHz (ranging from 11.4 GHz to 17.4 GHz) could also be achieved when the absorber thickness was only 2.0 mm. The samples exhibited low densities, strong microwave absorption performances and wide effective absorption bandwidths with thin absorber thicknesses, due to which they have a great potential as lightweight and efficient microwave absorbers.

Increasing attention has been focused on microwave absorption (MA) performance in the Ku band (12.4–18.0 GHz) due to the rapid development of radar, military aircraft and satellite communications. In this work, 2D heterostructure MoS2/graphene composites were proven to be promising full Ku band MA materials due to their superb characteristics of high dielectric loss, low density, large surface area and good thermal stability. By a simple one step solvothermal method, MoS2/graphene composites were successfully obtained, and the matched 2D structure between MoS2 and graphene could generate synergistic effects and maximize the MA properties. Only with 30 wt% of the as-prepared MoS2/graphene composites, excellent MA properties in wide frequency bands were obtained. An optimal reflection loss (RL) value of −41.9 dB was obtained at 16.1 GHz with a thickness of 2.4 mm and the RL values exceeding −10 dB were achieved in the whole Ku band (12.2–18.0 GHz) with a thickness of 2.6–3.0 mm.

Hierarchical hybrid nanostructures are desirable materials for microwave absorption (MA) capacity. However, how to obtain this kind of versatile structural materials still remains a great challenge. In this work, a novel MA composite of MnO2@NiMoO4 was synthesized via two-step hydrothermal processes combined with a simple annealing process. As confirmed by X-ray diffraction, scanning electron microscopy, energy-dispersive spectrometry, and transmission electron microscopy analysis, the well-defined NiMoO4 nanosheets could uniformly cover the surface of the MnO2 nanorods. Compared with pure MnO2 nanorods, these hierarchical composite structures could provide a higher superficial area, and more effective components, which will favor the penetration of microwaves into the absorber effectively instead of reflecting it, and then translate it into thermal energy. The minimum reflection loss (RL) value of MnO2@NiMoO4 composites was −31.4 dB at 11.2 GHz with a thickness of 3 mm, and the band of reflection loss was below −10 dB when frequency was in the range from 9.6 to 14.1 GHz. However, the minimum RL value of MnO2 was only −12.5 dB at 10.4 GHz with a thickness of 3 mm. The significantly enhanced microwave absorption of MnO2@NiMoO4 composites is mainly attributed to the hierarchical hybrid nanostructures, multi-effective components, good impedance matching, and interfacial polarization between MnO2 and NiMoO4. Meanwhile, the surface attached NiMoO4 is useful to increase the multiple reflection of electromagneticwaves. It is believed that these MnO2@NiMoO4 composites could serve as an excellent microwave absorber in practical applications.

Porous carbon has been expected to be a potential candidate as a lightweight and efficient microwave absorber. Nano-porous carbon carbonized directly from a walnut shell exhibits narrow microwave absorption frequency bandwidth, while the activation process can adjust the pore structure and optimize the microwave absorption performance. Herein, porous carbon materials were successfully prepared using walnut shells as precursors and ZnCl